Two of the four suicide bombers who attacked London last July 7 spent time at an Al Qaeda camp to prepare themselves for a suicide mission, the deputy leader of the terror network claimed in a video Friday.

British authorities previously said they knew Shehzad Tanweer and Mohammad Sidique Khan had visited Pakistan, but the comment from Al Qaeda No. 2 man Ayman al-Zawahiri was the first to claim that they had been at an Al Qaeda base.

"Both of them were seeking martyrdom and wished that they could carry out a martyrdom operation," al-Zawahiri said, using the Islamic euphemism for a suicide attack.

It was not possible to independently verify his claim, which was part of a video posted on the Internet on the first anniversary of the suicide bombings that killed 52 commuters on three subway trains and a bus in London.

Al-Zawahiri did not say where the Al Qaeda camp was, or when the two bombers trained there. But Al Qaeda is believed to have bases along the Pakistani-Afghan border, a rugged region where many experts think Usama bin Laden and al-Zawahiri may be hiding.

Al-Zawahiri said that while at the camp, Tanweer and Khan paid no heed to militants who discussed matters unrelated to suicide attacks, "because the goal for which they came to Al Qaeda's jihad base was to carry out a martyrdom operation."

A security analyst at the London think-tank Chatham House, Bob Ayers, said the claim stood in sharp contrast to a British police finding that there was no evidence linking the four London bombers to Al Qaeda.

"It makes the police look pretty bad," Ayers said. "It means the investigation was either wrong, or they had identified links, but were reluctant to reveal them."

The tape was released to coincide with the first anniversary of the bombings.

"The coordinated timing of the tape shows these guys did not act independently and were at a minimum supported by Al Qaeda if not recruited, trained and supported by them," Ayers said.

Spokesmen at the Foreign Office and London's Metropolitan Police said they were not aware of the tape.

Part of the video was recorded recently, since it included a statement from an Al Qaeda ideologue who, speaking English with a North American accent, referred to the June 30 revelation that U.S. troops allegedly raped and murdered an Iraqi teenager. The speaker's identity was unknown.

The tape, which appeared on an Islamic Web site known for carrying militant messages, was the full version of what Al-Jazeera television broadcast in edited form Thursday.

In that excerpt, Tanweer gave his motives for taking part in the London bombings and warned that the attacks would be only the beginning of a campaign of terror.

In the days after the London attack, terrorism experts suggested Al Qaeda may have played little or no role and said it was more likely the attackers acted locally and didn't need much money or expertise from overseas to wreak havoc.

A recent report by Britain's Home Office said the extent of any Al Qaeda involvement in the bombings remained unclear. It said there was "as yet no firm evidence" of Al Qaeda's involvement even though it had claimed responsibility for the attacks.

At the Tanweer family home in Beeston, West Yorkshire, 200 miles north of London, a front window bore a sign Friday telling journalists to stay away.

After an excerpt of the tape appeared on Al-Jazeera on Thursday, a friend of the family, Irshad Hussain, said Tanweer's relatives would be "devastated" to see the video.

"What you have witnessed now is only the beginning of a series of attacks that will continue and increase in strength until you withdraw your soldiers from Afghanistan and Iraq," Tanweer said in the excerpt broadcast Thursday.